1. Field of the Invention
The present invention relates to a planetary gear type multistage transmission for vehicles, which is installed between a prime mover and driving wheels in a vehicle such as an automobile, etc.
2. Description of the Related Art
In a vehicle, a planetary gear type multistage transmission has been widely utilized, which employs a plurality of planetary gear sets for selecting a plurality of transmission ratios or transmission stages determined in advance and engagement elements for connecting elements composing the plurality of planetary gear sets, such as clutches and brakes. For example, in an automatic transmission described in Patent Document 1, a forward multistage transmission of 12 stages has been achieved by using four sets of planetary gear sets. In an automatic transmission described in Patent Document 2 and 3, a forward multistage transmission of 6 stages has been achieved by using three sets of planetary gear sets. In an automatic transmission described in Patent Document 4, a forward multistage transmission of 7 stages has been achieved by using three sets of planetary gear sets. In an automatic transmission described in Patent Document 5, a forward multistage transmission of 10 stages has been achieved by using three sets of planetary gear sets. In an automatic transmission described in Patent Document 6, a forward multistage transmission of 7, 9 or 10 stages has been achieved by using three or four sets of planetary gear sets. In an automatic transmission described in Patent Document 7, a forward multistage transmission of 7 or 8 stages has been achieved by using four sets of planetary gear sets. In an automatic transmission described in Patent Document 8, a forward multistage transmission of 5 or 6 stages has been achieved by using two sets of planetary gear sets.
[Patent Document 1] JP-A 2002-206601
[Patent Document 2] JP-A H8-105496
[Patent Document 3] JP-A 2000-199549
[Patent Document 4] JP-A 2000-266138
[Patent Document 5] JP-A 2001-82555
[Patent Document 6] JP-A 2002-227940
[Patent Document 7] JP-A 2002-295609
[Patent Document 8] JP 2956173
However, it is desired that such a planetary gear type multistage transmission is not only simplified and small-sized with further multiple transmission stages secured and a wider transmission ratio width intended, but also the transmission ratio steps to be shifted are made into an equal ratio or made as close to an equal ratio as possible. There is a problem in that, in the automatic transmission disclosed in Patent Document 1 described above, the transmission ratio step is not made multiple in a convenient-to-use setting. For example, as shown in FIG. 5 of Patent Document 1, the transmission ratio steps in the sixth transmission stage and the seventh transmission stage are small to be 1.050, and arrangement of the transmission ratios is diversified to be large or small. In addition, although it is considered that the number of planetary gears is increased with respect to these problems, the entire length of the transmission is accordingly made longer, whereby its mountability thereof in a vehicle is worsened, and there is a possibility that engagement elements for connecting elements composing the planetary gear sets are increased in number. In particular, in the case of a so-called lateral installation in which the axial direction of an automatic transmission that is preferably used in an FF (front engine and front drive) vehicle and an RR (rear engine and rear drive) vehicle is determined in parallel to the axle, the limitation with respect to the entire length of the automatic transmission, which is regulated by the vehicle width, is severe in comparison to a case of a longitudinal installation, wherein there is a possibility that the installation becomes difficult.